Stabilisation of developed photographic images

ABSTRACT

EXPOSED AND DEVELOPED PHOTOGRAPHIC SILVER IMAGES CAN BE STABILISED BY TREATING THE LAYER CONTAINING THE EXPOSED IMAGE WITH A COMPOUND WHICH REACTS WITHTHE SILVER HALIDE IN THE UNEXPOSED AND UNDEVELOPED AREAS OF THE LAYER TO FORM A LIGHT-INSENSITIVE REATION PRODUCT. FADING OF THE SILVER IMAGES THUS PRODUCED IS PREVENTED BY PERFORMING THE DEVELOPMENT IN THE PRESENCE OF HETEROCYCLIC CARBOXYLYALKYL MERCAPTO COMPOUNDS.

United States Patent *Olfice 3,623,872 Patented Nov. 30, 1971 US. C].96-61 4 Claims ABSTRACT OF THE DISCLOSURE Exposed and developedphotographic silver images can be stabilised by treating the layercontaining the exposed image with a compound which reacts with thesilver halide in the unexposed and undeveloped areas of the layer toform a light-insensitive reaction product. Fading of the silver imagesthus produced is prevented by performing the development in the presenceof heterocyclic carboxylalkyl mercapto compounds.

Stabilisation of developed photographic images The invention relates toa process for the production of photographic images by exposure,development and subsequent stabilisation, development being carried outin the presence of heterocyclic carboxyalkyl mercapto compounds whichimprove the stability of the silver image even after prolonged storageunder extreme climatic conditions.

It is known to stabilise developed photographic images with complexforming compounds in rapid photographic reproduction processes as asubstitute for conventional fixing with sodium thiosulfate followed bywashing. In contrast to the method of fixing with sodium thiosulfate, inthese stabilizing processes the silver salts remain in the unexposed andundeveloped parts of the layer in the form of a light-insensitivereaction product of the stabilising compound with the original silverhalides. Stabilization of developed photographic materials has, however,certain disadvantages. One disadvantage is that nearly all substanceswhich form complexes with silver halides attack metallic silver andhence the photographic image, converting the silver into a complexcompound or simple silver salt. This leads to fading of the silver imageor to a change in the color of the image silver from black to a.brownish tone. This undesired elfect occurs particularly in a moistatmosphere.

Fading of the black image area can be prevented by adding to thestabilising bath heterocyclic mercapto compounds such as1-phenyl-S-mercaptotetrazole. However, the usual compounds of this typeare only sparingly soluble in the acid stabiliser solutions so that itis difiicult to apply a sufiicient quantity of these compounds. Theycannot be added in the required quantity to the emulsions because oftheir development inhibiting effect.

Fading of the black image areas can also be prevented by adding to theemulsion compounds which only decompose in alkaline solution to yield amercapto compound. Such compounds, however, cannot be added to theemulsion in sufiicient quantities to improve satisfactorily the keepingquality of the stabilised image on prolonged storage under extremeclimatic conditions.

It is among the objects of the present invention to provide compoundswhich do not show the disadvantages referred to above, and which arestabilising black silver images particularly upon prolonged storageunder extreme climatic conditions.

We now have found a process for the production of photographic imagesincluding the steps of exposing a supported silver halide emulsionlayer, developing and stabilising the exposed and developed layerwherein development is carried out with a bath which contains at leastone heterocyclic compound of the following formulae:

wherein n is 1 to 3.

Suitable compounds are summarized in the following table:

The preparation of these compounds is described in US. Patent No.3,330,663.

For operating the process according to the invention, conventionallight-sensitive photographic materials having at least one silver halideemulsion layer are suitable. The light-sensitive emulsions may containany silver halides, such as silver chloride or silver bromide, ifdesired with a small proportion of silver iodide. Emulsions which have ahigh silver chloride content are preferred.

The binders for the light-sensitive layers may be the usualwater-permeable layer-forming substances, particularly proteins,preferably gelatine.

Furthermore, the emulsions may contain alkylene oxide polymerisationproducts as chemical sensitizers. They may also contain the knownstabilizers.

In addition, the emulsions may contain developers or developercombinations of the type hydroquinone, pyrocatechol, aminophenol,compounds of the pyrazolidone series, phenylene diamine derivatives andthe like, antioxidants for the developer, e.g. potassium metalbisulfite,aldehyde and ketone bisulfite, matting agents and brightening agents.

Development is carried out in the usual manner, using known developers.According to a preferred method of carrying out the invention, thedeveloper is added to the photographic material and development isinitiated by treatment with an alkaline aqueous bath, hereinafterreferred to as an activator bath.

The concentration of the compounds for use according to the invention inthe development bath may vary within wide limits. The concentrationdepends upon the photographic material used and the nature of thedeveloper. The optimum concentrations for a particular reproductionprocess can be determined by a few simple laboratory tests. Amounts of0.5 to 10 g. per liter of treatment bath, preferably 1 to 5 g. perliter, have generally been found to be sufficient.

Suitable stabilising agents, i.e. compounds which are capable ofconverting the silver halide remaining after development into a compoundwhich is not sensitive to light, have been described e.g. in BritishPatents Nos. 631,184 or 959,807 and in U.S. Patent No. 2,525,532 orFrench Patent No. 1,237,454. Ammonium thiocyanate, and alkali metalthiocyanates, e.g. sodium or potassium thiocyanate, have been found tobe particularly suitable.

These stabilising baths may also contain the usual other additives suchas alkali metal sulfites or metabisulfites or cycloalkanone bisulfites,acetic acid or its salts and organic compounds, particularly additionalheterocyclic compounds which contain mercapto groups, such as l-phenyl-S-mercaptotetrazole, which form sparingly soluble silver salts.

3 EXAMPLE 1 A light-sensitive photographic material comprising asupported silver chloride gelatin emulsion layer which emulsion layercontains 0.2 mol of silver halide with a silver iodide content of lessthan 0.1 mol percent of silver iodide per kg. of emulsion (amount ofsilver in the form of silver halide 1.3 g./m. and hydroquinone (12 g. ofhydroquinone per kg. of emulsion) is exposed to form an image anddeveloped in the following activator solution:

50 g. of sodium hydroxide 40 g. of anhydrous sodium sulfite 2 g. ofpotassium bromide 1 g. of 1-phenylpyrazolidone-(3) made up to 1 literwith water.

The compounds shown in the following table are added to the aboveactivator solution. The quantities added are shown in the table.

The developed material is then treated with the following stabilisingsolution:

250 g. of ammonium thiocyanate 145 g. of potassium metabisulfite 100 ml.of a 3% aqueous solution of formaldehyde 25 ml. of 60% acetic acid,

made up to 1 liter with water.

The samples are processed in a two-bath development apparatuscustomarily employed. The treatment time is about 1 t 5 seconds in theactivator bath and about 2 to seconds in the stabilising bath.

To test the stability in storage of the silver image, a portion of thecopy is kept over water in a vessel for 24 hours.

Several of these uniformly moist portions of the copy are inserted intoa polyethylene container and this container is placed in a bagcontaining 30 ml. of water and sealed. The sealed containers are storedin a heating cupboard at 60 C. for 5, 24 and 48 hours, respectively, andthe change of the silver image which has taken place after this time isexamined.

Whereas the silver image of the copies produced according to theinvention remains black or dark brown to black depending on the time ofstorage, under the above condition the comparison sample showsdiscoloration varying from brown to pale brown. The maximum density of.4 the various fresh, air-dried materials and those which have beenstored in moist heat is measured in a densitometer. The followingresults are obtained:

TABLE Maximum density after storage Concenin moist heat for- Compoundadded tration, Air N o. g./l. dried 5 hours 24 hours 48 hours We claim:

1. A process for the production of photographic images by exposure of aphotographic material which has at least one silver halide emulsionlayer, development and stabilisation of the unexposed and undevelopedsilver halide, wherein development is performed with a bath containingat least one compound of the following formula or salts thereof:

References Cited UNITED STATES PATENTS 3,330,663 7/1967 Weyde 96-114.3

NORMAN G. TORCHIN, Primary Examiner M. F. KELLEY, Assistant Examiner US.Cl. X.R. 96-66, 95

